1. Field of the Invention
The present invention relates to an optical recording medium and a manufacturing method thereof, and specifically, to an optical recording medium having an inorganic recording layer.
2. Background Art
In the past, CDs (Compact Discs), DVDs (Digital Versatile Discs), and the like have led the optical recording media market. However, recently, with the higher definition of televisions and the exponential increase of data handled in PCs (Personal Computers), higher capacity optical recording media have been demanded. In response to the demand, high-capacity optical recording media such as BDs (Blu-ray Discs (registered trademark)) for blue laser have appeared and a new market of high-capacity optical recording media has been created.
As recordable optical recording media, there are rewritable optical recording media represented by DVD-R (Digital Versatile Disc-Recordable) and DVD±RW (Digital Versatile Disc±ReWritable), and recordable optical recording media represented by CD-R (Compact Disc-Recordable) and, DVD-R (Digital Versatile Disc-Recordable), and particularly, the latter has greatly contributed to the market growth as low-price media. Therefore, it is conceivable that the price reduction of the recordable optical recording media is also necessary for market growth in high-capacity optical recording media for blue laser.
In the recordable optical recording media, both inorganic materials and organic dye materials are approved as recording materials according to the standards. The recordable optical recording media using organic materials have an advantage that they can be manufactured at low cost by a spin coating method, and, on the other hand, the recordable optical recording media using inorganic materials have an advantage in reproduction durability and good push-pull signal characteristics, but have a disadvantage in necessity of a large-scaled sputtering system. Therefore, in order that the recordable optical recording media using inorganic materials become competitive with those using organic materials in terms of price, it is absolutely necessary to suppress the initial investment of manufacturing equipment and efficiently produce recording media by improving takt time per disc.
As the most effective means for solving the problem, the initial investment for a sputtering system may be suppressed the manufacturing takt time may be shortened by reducing the number of layer forming a recording film and the number of deposition chambers may be reduced. However, even when the number of layers is simply reduced, if a material having a large thickness and a slow deposition rate is used, the manufacturing takt time may increase and the cost rise may be caused instead.
In related art, as a material for a protective layer of the recordable optical recording media using inorganic materials, a transparent dielectric material such as SiN or ZnS—SiO2 is mainly used (for example, see Patent Document 1: JP-A-2003-59106). However, SiN and ZnS—SiO2 have advantages in higher deposition rate and good productivity, but have a problem in poor storage characteristics (storage reliability). Of the dielectric materials other than those mentioned above, some have high storage reliability, however, these materials have problems that the deposition rate is very low and the productivity is poor because radiofrequency (RF) sputtering is necessary. Therefore, it is difficult to achieve a balance between storage reliability and productivity.
In order to solve the problem, a technology using an indium oxide and a tin oxide (hereinafter, referred to as ITO) that can be DC-sputtered as a protective layer has been proposed (for example, see Patent Document 2: JP-A-2009-129526). In this technology, high storage reliability may be realized in the recordable optical recording media and high productivity may be obtained by reducing the number of deposition chambers at the same time. That is, using ITO for the protective layer, the high deposition rate may be obtained and the protective layer may be thicker by only one chamber, and, as a result, the number of chambers may be reduced while the degree of freedom of design is kept.